The present invention relates to machines for grinding saw chains and more particularly to a machine for grinding the depth gauges of saw chain cutter links.
Saw chains typically include alternating right- and left-hand cutter links of similar but opposite configuration interconnected by drive links and tie straps. Each cutter link includes a generally L-shaped cutter tooth or blade with top and side cutting edges and a depth gauge ahead of the cutter tooth to limit the depth of penetration of the top cutting edge into the wood. There is a predetermined desired vertical distance or "clearance" between the top cutting edge and the top of the depth gauge. With repeated sharpenings of the cutting edges, the cutter tooth becomes shorter. However, because the cutter tooth has a clearance angle, or backslope, along its top surface, the top cutting edge becomes lower on the link as the tooth becomes shorter, thereby reducing depth gauge clearance. Thus, as the tooth becomes shorter, the height of the depth gauge should be reduced so as to maintain a desired clearance.
In the past, depth gauge clearance has been maintained most often by hand filing. File guides have long been available for this purpose. Typically, the file guide is supported on top of the cutter tooth and extends forwardly therefrom over the depth gauge with a slot in the guide through which an upper portion of the depth gauge protrudes if the depth gauge is too high for a given height of cutter tooth. The user then simply wipes a flat file across the file guide to remove the protruding metal from the top of the depth gauge until the depth gauge is flush with the guide surface. Typical such file guides are shown, for example, in U.S. Pat. Nos. 2,622,338; 2,705,376, and 3,365,805.
Others have devised power grinders for grinding depth gauges to a desired height relative to its cutter tooth. Silvey U.S. Pat. No. 3,717,051 discloses a depth gauge grinder which has been made available commercially in both manual and automatic versions. In such grinder, the grinding wheel is preset to grind a desired clearance by measuring from the top of a selected cutter tooth. Then all depth gauges on the saw chain are ground with the grinding wheel at the same preset position. If the cutter teeth of all cutter links of the saw chain are of about the same length so that the top cutting edges of the cutter teeth are all at about the same height, such grinder will grind all depth gauges to about the same clearance. However, many persons who use and sharpen saw chains do not always maintain all cutter teeth of their saw chains at about the same length, although this is highly recommended. Where different cutter teeth of a saw chain are of widely differing lengths, the Silvey grinder will produce different depth gauge clearances on different cutter links depending on the length of the tooth.
Other depth gauge grinders have been devised which determine depth gauge clearance by measuring or indexing from the top of each cutter tooth. For example, Granberg U.S. Pat. Nos. 3,796,113 and 4,002,089 disclose a power-operated depth gauge grinder for use in grinding depth gauges while the saw chain remains on the bar of the chain saw. A guide plate attached to the grinder is supported on the top of the cutter tooth of the cutter link while the grinding element lowers the depth gauge of the same link as determined by the vertical distance between the bottom surface of the guideplate, and the grinding surface of the element.
Ziegelmeyer U.S. Pat. No. 4,267,751 discloses a power-operated depth gauge grinder which operates on a principle similar to that of the aforementioned Granberg patents but with the saw chain removed from the chain saw bar and mounted on the saw chain support of a grinding machine. As each cutter link is advanced toward the grinding wheel, the top of the cutter tooth of such link engages a preset guide plate which depresses the saw chain support so that a depth gauge is brought into contact with the grinding wheel at an elevation that will grind the depth gauge to the desired preset clearance. Thus, the Ziegelmeyer device, like those of Granberg and prior file guides, determines depth gauge clearance for each cutter link by indexing from the cutter tooth of the same link.
The advantages of the hand file guides and prior Granberg and Ziegelmeyer depth gauge grinders over, for example, the aforementioned Silvey depth gauge grinder, is that the former will produce a fairly uniform depth gauge clearance on all cutter links of a chain regardless of wide variations in the lengths of the cutter teeth of that chain. However, they have no advantage over the Silvey depth gauge grinder in instances where all cutter teeth of a saw chain are maintained at approximately the same length, as recommended.
All of the aforementioned types of power-operated depth gauge grinders and all other known depth gauge grinders have two principal drawbacks.
First, depth gauge grinders of the Granberg and Ziegelmeyer types have guide plates or indexing means which rub across the top cutting edge of the cutter tooth during the grinding operation and therefore have a tendency to dull the previously sharpened cutter tooth. In this regard, it is universal practice to sharpen the cutter teeth before lowering the depth gauges so that the depth gauge clearance is determined relative to the sharpened cutter tooth with which it works.
Second, none of the aforementioned depth gauge grinders provide for any automatic compensation to increase depth gauge clearance as the cutter tooth becomes shorter. Experts in sharpening saw chain agree that as a cutter tooth becomes shorter with repeated sharpenings, depth gauge clearance should be increased to compensate for the increasing longitudinal distance between the depth gauge and the cutting edge. As a saw chain travels at high speed about a saw bar, there is a tendency for the forward end of each cutter link to ride higher than the rear end. This is caused by two factors. One is the tendency of the rear end of the lower edge of a cutter link to wear faster than the forward end. The other is the tendency of the forward end to be lifted as it is pulled about the saw bar. The combination of this lifting effect on the forward portion of the cutter link and the greater wear on the rear lower edge in effect raises the depth gauge relative to the cutting edge of a link, producing an effective reduced clearance which becomes more noticeable as the distance between the depth gauge and the cutting edge increases. To compensate for this, some experts advise that the measured depth gauge clearance on a cutter link with a worn cutter tooth should be up to ten thousandths of an inch greater than on a link with a new cutter tooth. None of the aforementioned depth gauge grinders automatically compensate for this need for increased clearance as the cutter tooth wears back.
Third, none of the aforementioned depth gauge grinders are capable, without adjustment, of providing the right-hand cutter links with a different depth gauge clearance than the left-hand cutter links of the same chain when desired. In practice, it has been found that with chain saws on which the motors are offset on the left-hand side of the saw bar, as is commonly the case, the saw chain tends to run to the right when cutting wood. It is believed that the reverse effect would be true if the motor is offset to the right-hand side of the saw. To compensate for the tendency of a saw chain to "run to the right", which means the left-hand cutters are outcutting the right-hand cutters of the saw chain, the clearance of the depth gauges of the left-hand cutters should be reduced or the clearance of the right-hand cutters increased. None of the mentioned power depth gauge grinders are capable of accomplishing this without an adjustment of the grinding machine itself.
Accordingly, there is a need for a power-operated depth gauge grinder which overcomes the aforementioned drawbacks of prior power grinders while maintaining their advantages of fast and accurate depth gauge grinding.
A primary objective of the invention, therefore, is to provide a depth gauge grinding machine which automatically increases the depth gauge clearance of a cutter link as the cutter tooth of that link becomes shorter through repeated sharpenings.
Another primary object of the invention is to provide a depth gauge grinder as aforesaid which is capable, without adjustment, of grinding the depth gauges of the right-hand cutter links to a different clearance than the depth gauges of the left-hand cutter links.
Still another primary object of the invention is to provide a depth gauge grinder as aforesaid which determines depth gauge clearance by gauging from the top cutting edge of its associated cutter tooth, but without any direct rubbing contact between the gauging or indexing means and the cutting edge so that the cutting edge will remain sharp during the depth gauge grinding operation.
Other objectives of the invention are to provide a depth gauge grinder as aforesaid which is simple to operate, has a minimum of adjustments, is economical to operate and maintain, and is adaptable to automatic operation.
Still another objective is to provide a depth gauge grinder as aforesaid which does not require the indexing means to remain in contact with the top of the cutter tooth while the depth gauge is ground.
The foregoing and other objects, features, and advantages of the present invention will become apparent from the following detailed description which proceeds with reference to the accompanying drawings.